Manufacture of pulp, etc.



patented Feb. 21,

iearaiur or iec LINN BRADLEY, OF MONTCLAIR, NEWJERSEY, AND EDWARD'P.MCKEEFE, OF PLATTS BURG', NEW YORK, ASSIGNGRS T BRADLEY-MGKEEFECORPORATION, OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK MANUFACTURE OF PULP, ETC.

No Drawing. App1ication filed May 14, 1924,

This invention relates to improvements in the production of chemicalpulp from wood (both coniferous and non-coniferous) whereby a good yieldof'chemical pulp can be 5 obtained.

The invention also includes "a new cooking liquor for the cooking ofwood,as well as the new and improved pulp-making or cooking operationitself for the production of the pulp from the wood; and it includes theresidual liquors produced by the pulpmaking operation; and also itincludes the new pulps and the new papers madetherefrom. It alsoincludes a new and improved method of regeneration of cooking liquors,

and improvements in the process of treating the residual liquors; aswell as a regenerative process for the regeneration of the cookingliquor and the carrying out of a successive 0 cooking operation wit-hthe regenerated cooking liquor.

According to one embodiment of the present invention wood is subjectedto a cooking operation under pressure and at an elevated temperaturewith a cooking liquor containing an oxygen-bearing alkaline compound, e.g., caustic alkali, a trioxy-sulfur-bearing compound, e. g., an alkalithiosulfate and an alkali sulfide. The cooking liquor may also I containother constituents such as sodium carbonate, sodium sulfite, etc.

The new pulp-making or cooking process of the present invention may beconsidered as a modification of the so-called sulfate proc ess. In thesulfate process, the cooking operation is carried out with 'a cookingliquor containing essentially caustic soda and' so dium sulfide. In theprocess of the present invention the cooking liquor contains causticsoda. sodium sulfide and sodium thiosulfate, advantageously with theamount of sodium present in the sodium hydroxide and in the sodiumsulfide being larger than that at present in the sodium thiosulfate.

In the process of making chemical, pulp from wood according to thepresent invention. the wood may be freed from bark, chipped and thensubjected-to a cooking operation under pressure and at an elevatedtemperature with the new cooking liquor.

Serial No. 713,257. Renewed July 13, 1932.

Woods of various kinds can be treated for the production of chemicalpulp by the proc ess of the present invention, and such pulp can beproduced therefrom. The cooking liquor containing the caustic soda,sodium thiosulfate and sodium sulfidemay advantageously be produced fromresidual liquor from a pulp-making operation, in one or another of thevarious methods of treatment hereinafter described. The cooking liquorcan, however, be produced in any suitable manner, and additionalchemicals to supplement or modify that regenerated from residual liquorscan also be supplied in any suitable manner.

In producing the cooking liquor in the first instance, a solutioncontaining caustic soda and sodium sulfide may beused, and someelementary sulfur dissolved therein to form a solution containingcaustic soda together With-a regulated amount of sodium sulfide orpolysulfide or both. Normal sodium sulfite can be added to this solutionin regulated amounts to react with the loosely combined sulfur of anypolysulfide present to form sodium thiosulfate. Instead of producing thecooking liquor in this way, sodium thiosulfate may be preparedseparately and added to a solution containing caustic soda and sodiumsulfide.

Sodium suliite in solution may be converted into thiosulfate by reactionwith free or loosely combined sulfur, e. g. by a polysulfide or withelementary sulfur. The latter may be added in finely divided form andthe solution heated to aid in the solution of the sulfur. Sulfur may beobtained also by decomposition of a sulfide or polysulfide, of sodiumand some of this sulfur taken up by sodium sulfite. A mixture of sodiumsulfite and sodium sulfide may be treated with sulfur dioxide or sodiumbisulfite and produce sodium thiosulfate in solution. A mixture ofsodium carbonate and sodium sulfide or polysulfide may be treated withsulfur dioxide or sodium bisulfite and leave some sodium thiosulfate insolution. In case the carbonate is present in 5 too great an amount forthe quantity of sulfide or polysulfide the resulting sulfited solutionmay also contain some sodium sulfite.

' precipitation of calcium sulfate or carbonate,

leaving sodium sulfide or polysulfide or both in solution. By heatingsulfur and an excess of lime with a solution containing a. sufficientamount sodium carbonate, the lime will causticfze some of the sodiumcarbonate and convert it into caustic soda so that the solution willthen contain caustic soda in addition to sodium sulfide or polysulfide.Sodium thiosulfate, sodium sulfite, etc, may be produced therein oradded thereto in such amount as may be desired.

It is particularly advantageous, however, to produce the cooking liquorof the process of the present invention by treatment of the residualliquor produced by the cooking operation of the process. The process canbe carried out to a large extent, for example, in a mill such as is nowused for carrying out the so-called sulfate process. The residual liquorcan be concentrated, the concentrated or dried product then subjected tocarbonization or charring, and the resulting material can be subjectedto a further operation to give a melt or smelt containing considerableamounts of sodium carbonate and sodium sulfide. By dissolving this melta solution is obtained containing the sodium compounds.

The solution so obtained, and containing sodium carbonate and sodiumsulfide can then be subjected to treatment with a regulated amount ofsulfur dioxide or sodium bi sulfite or both, and of elementary sulfur asneeded or desired to convert part of the soda content into thiosulfate,and to give a solution containing sodium carbonate, sodium thiosulfate,and a sulfide of sodium. This solution can then be subjected tocausticizing with lime to convert some of the sodium carbonate intocaustic soda. thus giving a solution containing caustic soda, sodiumthiosulfate and a sulfide of sodium.

The amounts and proportions of sodium hydroxide, sodium thiosulfate andsodium sullide used in the cooking liquor may be varied considerably.The amount of caustic soda may be the same as that ordinarily used inthe sulfate process, but it may advantageously be considerably less thanso used, while in certain cases it may be even somewhat greater than theamount ordinarily used in the sulfate process. The sulfide content ofthe cook: ing liquor, particularly with decreased caustic soda contentin the liquor, may be as great as or even greater than that ordinarilyused in the sulfate process; although when the amount of caustic soda islarger than that ordinarily used in the sulfate process the amount ofsulfide will generally be less and may be considerably less, because ofthe thiosulfate content of the liquor. Sodium thiosulfate will also bepresent in the various cooking liquors in considerable amount, and thisamount may vary. Particularly when dense hard woods are used whichrequire a relatively large amount of chemical in the cooking liquor, theamount of caustic soda based upon the total weight of the Wood canadvantageously be regulated to a point where the wood will not beovercooked or injured to an objectionable degree, and the presence ofthe sulfide and thiosulfate in suflicient amounts will neverthelessenable the cooking operation to be carried to completion. Sodiumthiosulfate appears to react in a somewhat different manner than sodiumsulfide, and the combined actions of the thiosulfate and sulfidetogether with caustic soda is such that the action of the caustic sodais advantageously supplemented by the sulfide and the thiosulfate. Theamount of the thiosulfate may be equal-to or greater than the amount ofthe sulfide, although in some cases the amount of thiosulfate may beless than the amount of sulfide.

It is one advantage of the present inven tion that it may be carried outin the plant and with the equipment of existing sulfate mills,requiringbut moderate change both in the mill construction and in the generalmethod of operation. The cooking, concentrating or evaporating,carboni'zing or calcining, and smelting operations may be carried out inthe apparatus now used in the socalled sulfate-process, although theseoperations will be changed or modified by the different character of thecooking liquor employed and the different nature of the residual liquorproduced, and in the treatment of the residual liquor for the productionof a further amount of cooking liquor therefrom.

One of the important characteristics which the present inventionpossesses is that it is applicable to the treatment of various kinds ofwood, both coniferous and non-coniferous, including various woods thatare commonly considered as inferior for the production of satisfactorychemical pulp therefrom. The rapidly decreasing supply of wood suitableand available for pulp-making purposes, according to the usual presentday processes, and the high cost of equipment and operation of chemicalpulp mills, makes it of industrial and economic importance to increasethe yield of chemical pulp from woods which are commonly used forpulp-making purposes and to make available for pulp-making purposeswoods ordinarily considered of little or no Value for the production ofhigh grade pulp.

The process of the present invention is ap plicable not only to thecommon pulp woods, such as poplar and spruce, but also to various otherwoods, both coniferous and, lion-cniferous, which are not commonlyincluded among the pulp woods. Non-coniferous woods, including the heavydense hard woods, such as birches, beeches and maples, the differentkinds of oak, hickory, eucalyptus, elm, ash, etc, may be used as well aspoplars,

aspens, bass wood, cotton wood, chestnut,

gums, etc. So also coniferous woods may be used, including not onlyspruces, firs, and balsam, but also hemlocks, cedars, cypress, larches,tamarack and the various pines. Pines of a resinous character, such aswhite pine, ack pine, longleaf pine, shortleaf pine, lodgepole pine,slash pine, and other similar pines can thus be treated according to thepresent invention for the production of suitable chemical pulptherefrom.

The cooking operation of the present invention can be carried outindigesters of the type now used, for example, in the soda or sulfateprocesses. The digesters of present day sulfate mills can advantageouslybe used. The provision of an acid-resisting lining in the digester isnot necessary, but ordinary iron or steel digesters, preferably forge orhammer welded, can be used. The digesters may be heated and the cookingliquor circulated therein in any suitable manner. Outside circulation ofthe cooking liquor from the bottom of the digester with reintroductionat the top through a suitable distributor can be employed, and withsuitable heating of the cooking liquor which is being circulated. Rotarydigesters may be used with distinct advantage.

In carrying out the cooking operation, different temperatures may beemployed, for example, a temperature corresponding to a saturated steampressure of 100 to 125 lbs. saturated steam. gauge pressure, atemperature around 338 to 353 F.; or the temperature may be higher orlower than this.

The cooking liquor may contain, for example, for poplar wood, from l0 to60 grams per liter of caustic soda, from to grams per liter of sodiumthiosulfate and from 15 to -14) grams per liter of sodium sulfide,although these amounts a'nd relative proportions can be varied. Forconiferous or resinous woods such as spruce, jack pine, slash pine. etc,the cooking liquor may contain, for example. from $0 to grams per literof caustic soda. from 10 to 25 grams per liter of sodium thiosulfate.and from 20 to 45 grams per liter of sodium sulfide. In general. thetotal sodium content of-the cooking liquor should be at least 1271.: onthe bone dry weight of the wood cooked. it may range from 12 to 20ft.

In carrying out the process of the present invention, the procedure maydiffer some- Ordinarily all? what with non-coniferous woods, andparticularly dense hard woods such as blrches,

beeches, and maples, etc.,and with less dense woods such as poplars,etc, or with coniferous woods such as spruces, some pines, etc. Withnon-coniferous woods, for example, the digester charge may be heated ina relatively rapid manner to the cooking temperature while withconiferous woods it is advantageous to heat up the digester charge moregradually so as to secure fairly thorough penetration of the wood chipswith the cooking liquor at a moderate temperature before heating thecharge to the higher cooking temperature.

lVith the dense heavy hard woods which have a much greater weight ofwood per cubic foot, the digester charge, if the digester is filled withthe hard wood chips, will be far greater in weight and in wood contentthan with the soft and less dense coniferous woods or woods such aspoplar. T he increased weight of these dense hard woods will require agreatly increased amount of chemical per digester charge forsatisfactory cooking. If the amount of caustic soda in the cookingliquor is too great, the wood chips will be injured; but the presentinvention presents the advantage that the amount of caustic soda can bekept below the point which will injure the chips and the pulp to anobjectionable degree, and the action of the caustic soda will be sosupplemented by the sodium sulfide and sodium thiosulfate that asatisfactory cooking operation can nevertheless be obtained, the amountof sulfide and thiosulfate being sufficient to supplement the action ofthe caustic to give the desired cooking action upon the wood chips.

hen the cooking operation is completed, the charge. can be blown into ablow pit, the residual liquor recovered and the pulp washed andsubjected to further treatment in a manner customary in the subsequenttreatment of chemical pulp either for the manufacture .of merchantablepulp or for the manufacture of paper or other products therefrom.

The pulps produced by the. process of the present invention are somewhatdifferent in character from the pulps commonly produced by the usualmethods, and we accordingly regard the pulps as new and improved pulps.Various pine woods, such as, for example, slash pine, jack pine, etc. aswell as spruces, tamarack, hemlock and other coniferous woods, may betreated according to the process of the present invention to yield pulpsof excellent strength. It will be evident, however, that inasmuch asdifferent woods differ from each, other in their fibre structures, thepulps produced therefrom will differ somewhat from each other. Theprocess of the present invention accordingly will give different kindsof pulp from different kinds of wood, each wood being more or lesscharacteristic in the pulp which it gives.

The residual liquors produced by the process of the present inventionare of characteristic composition and properties. Our investigation ofthe chemical reactions which take place during the cooking of woodsleads us to believe that the wood substance is a complex reactivechemical substance which reacts with the chemicals contained in thecooking liquor, and that the nature of the reactions and of the reactionproducts produced varies with the cooking liquor employed. Sodiumthiosulfate,-when present in appreciable amounts in the cooking liquor,reacts in a characteristic way with the reactive constituents or groupsof the wood substance, and when both sodium thiosulfate and sodiumsulfide, together with caustic soda, are present in the cooking liquor,the combined reactions of these various chemical substances upon thereactive substances results in the production of a residual liquorcontaining the reaction products of these various chemicals with thereactive substances. The residual liquors contain the soluble reactionproducts of these chemical reactions.

These residual liquors can advantageously be treated for theregeneration of further amounts of cooking liquor therefrom for solutioncan then be treated for the production of further amounts of cookingliquor therefrom; Vhen the residual liquor from the pnlpmaking operationis evaporated to dryness, and carbonized to destroy organic'matter. andthe resulting carbonized product is subjected to a smelting operation,the solution of the resulting melt or smelt generally containsconsiderable amounts of sodium carbonate, and of sodium sulfide, and itmay contain other sodium compounds such as sodium sulfate, sodiumthiosulfate, sodium sulfite, etc. Part of the sodium sulfide may bepresent as polysulfide or as polysulfides.

The concentrating, carbonizing and smelting operations can. as abovepointed out, be carried out in a sulfate mill, with little if anyalteration in the equipment of such a sulfate mill. Furthermore,additional amounts of a sulfate of sodium can be added to the residualliquor before carbonizing or to the carbonized product before smelting,and the amount of the sodium sulfide. or of sodium sulfide andpolysulfide, can thereby be increased in the resulting melt. Thecarbonized or charred p"oduct from the carbonizing or charring furnacemay also have additional carbonareaders ceous material added thereto ifnecessary or desirable for the smelting operation.

The melt or smelt produced in the present process, somewhat like themelt or smelt from the snielte: of the sulfate-process, containsrelatively large amounts of sodium sulfide or of sodium sulfide andpolysulfide or polysulfides. In the sulfate process, all of this sulfideusually is employedv again in the cooking operation, after causticizingthe solution to convert some of the sodium carbonate into caustic soda.In the process of the present invention, however, apart of the sodiumsulfide may be convertedinto sodium thiosulfate, or the solution of themelt may be treated to convert loosely combined sulfur of thepolysulfide, when present, int-o sodium thiosulfate.

The solution of the melt or a portion thereof, may, for example, betreated directly with sulfur dioxide in regulated amount. Some sulfurdioxide mayreact with sodium polysulfide, when present, or with sodiumsulfide, or loth, with the production of sodium thio sulfate. Thesolution can in this way be substantially freed from polysulfide, andthe amount of sodium sulfide also can be reduced and part of itconverted into sodium thiosulfate, and this conversion can be regulatedby regulating the sulfur dioxide treatment.

In tead of treating the solution of the melt or a portion thereof withsulfur dioxide it can be treated with sodium bisu'lfite or acid sodiumsulfite, or with sodium sulfite and sulfur dioxide. and the amount ofsuch reagents and the treatment can be regulated and cont-rolled to givea solution containing a regulated amount of sodium thiosulfate.Elementary sulfur may be added, if needed, to convert sulfite intothiosulfate.

Instead of treating the solution of the melt with sulfur dioxide or acidsodium sulfite, it may be treated with normal sodium sulfite, which willreact with loosely combined sulfur of the polysulfide if any present toform sodium thiosulfate, and this'treatment may be supplemented by afurther treatment of a portion of the solution, if desired, with sulfurdioxide or sodium bisulfite to produce a further amount of thiosulfate.Added sodium compounds and sulfur can be introduced for further use inthe carrying'out of the cooking operation, for example, to make up fortheir losses in the operations. Additional sodium can also beintroduced, for example. in the form of a sulfate of sodium at somepoint prior to the smelting operation. This sodium sulfate will bereduced to a greater or less extent to sodium sulfide, and this sulfide.for example, by reaction with sulfur dioxide in solution, can beconverted at least in part into sodium thiosulfate.

In subjecting the solution ofthe melt to a sulfiting operation, as abovedescribed, this sulfiting operation is regulated and limited.

iii)

eeaoie if an excess of sulfur dioxide or sodium acid. sulfite wereemployed, all of the sodium sulfide would be converted into sodiumthiosulfate or other compounds and little or no sodium sulfide would beleft, and the resulting solution on causticizing might then containlargely caustic soda, sodium sulfite and sodium thiosulfate. In theprocess of treating the residual liquors according to the presentinvention, the solution of the melt is not sulfited to such an extent asto react with all of the sulfide, but part of the sulfide is left in thesolution and a part is converted into thiosulfate. and the relativeamount of sulfide and thiosulfate can be regulated and controlled byregulating and controlling the operations, especially When one portionis sulfited, the other portion causticized and the two portionsthereafter mixed.

After the sulfiting operation, the solution of the melt or theunsulfited portion thereof may be subjected to causticizing With lime,in a manner similar to that practiced in the presentday sulfate-processfor treating the solution of the melt to regenerate a cooking liquorcontaining caustic soda and sodium sulfide. 'l he causticized liquoraccording to the present invention, however, will contain both sodiumsulfide and sodium thiosulfate, in addition to caustic soda especiallywhen the two portions are separately treated and then mixed together.

Instead of subjectingthe solution of the melt to sulfiting and then tosubsequent causticizing with lime, the solution may first be subjectedto causticizing with lime, and then subjected to a regulated sulfitingoperation. The causticizing with lime is usually incomplete, some sodiumcarbonate being left behind in the solution. During the sulfitingoperation some of the sodium carbonate may be converted into sodiumsulfite, which may in turn react with loosely combined sulfur of thepolysulfide, if any is present, to form sodium thiosulfate. When thecausticized solution is sulfited with sulfur dioxide, the sulfur dioxidemay react first with the caustic soda to form sodium sulfite, and someof this may then react with loosely combined sulfur of the polysullideifany to form sodium thiosulfate. Sulfur may be added to convert l ?a SOinto Na t a O if necessary or desired. instead of subjecting theresidual liquor to evaporation to dryness, carbonizing, and subsequentsmelting. the smelting operation may be omitted, and the dried residuefrom the drying of the residual liquor can be sub jected to a regulatedcarbonizing or calcining operation, for example, in a rotary furnacesuch as is used in the soda process mills, and the carbonizing operationcan be carried out so as to give a furnace productfrom which a solutioncan be obtained containing sodium carbonate and some sodium sulfide,

together with varying amounts of sodium thiosulfate, sodium sulfate,etc, and the resulting solution can then be subjected to a subsequentcausticizing operation of the character above described. These liquorsmay also be given a regulated sulfur treatment if desired or necessary.

The regulated sulfiting operation can be carried out, for example, byrunning the solution of the recovered soda compounds or a portionthereof through a suitable tower into which a regulated amount of"sulfur dioxide is introduced. The resulting solution or the otherportion thereof can then be run to the causticizing tank for treatmentwith lime to causticize sodium carbonate to produce caustic soda. Theadded reagents required to make up for those lost in the process may besupplied by lime, e. g. for the causticizing, sodium carbonate, e. g. byadding to the solution of the melt before causticizing, or sodiumsulfate or bisulfate e. g. for adding to the residual liquor or dried.product before smelting, and sulfur or sulfur dioxide or all of thesematerials;

@ther suitable compounds may be used in the production of a regeneratedcooking liquor for the process herein. Sodium car bonate may be used andsubjected to causticizing, or sulflting, etc. to furnish additionalsodium hydroxide or sodium sulfite or sodium thiosulfate. Calciumcarbonate may be burned to form the oxide and this used for convertingsodium carbonate in solution into caustic soda. Elementary sulfur orsulfur dioxide may be used for introducing sulfur when the othersulfur-bearing compounds are not adequate for furnishing the desiredsulfur content in the cooking liquor.

When the cooking liquor contains a smaller amount of caustic soda thanin the ordinary sulfate process cooking operation, and correspondinglylarger amounts of sodium-sulfur compound or compounds,the cookingoperation may advantageously be carried out at a somewhat higher.temperature than usual, especially when the amount-of thiosulfate orsulfite is quite high as compared with the sulfide. Y

Coniferous Woods and non-coniferous Woods'behave somewhat differently,but in general the non-coniferous woods are more easily pulped than theconiferous, and since they also contain relatively shorter or smallerfibres, greater care should be taken in the cooking operation to avoidexcessive injury. By carefully cooking, non-coniferous Wood pulp can beobtained Which is quite strong and useful in making relatively strongpapers.'

Another modification of the process of this invention Where long fibredWoods are cooked with a liquor Which contains caustic soda, sodiumthiosulfate and sodium sulfide, is to concentrate the residual liquorfrom the cooking operation to some extent, for example to about 20 to 25B. at about 135 F., and then subject the concentrated residual liquor toa regulated sulfiting treatment, e. g. with sulfur dioxide or withsodium bisultite or both, to convert a considerable portion of thecontained soda compounds into sodium sulfite together with some sodiumthiosulfate. The residual liquor usually contains a fair amount ofsodium thiosulfate, and may also contain some sodium sulfide. Thelatter, upon sulfiting may be converted to a considerable extent intosodium thiosulfate. By rendering the partially concentrated liquorslightly acid to litmus, considerable organic matter is precipitatedfrom the solution. When the liquor is warm enough this or ganic mattercoagulates, some of it settles and in some cases some of theprecipitated organic matter floats to the top of the liquor. The liquormay be withdrawn so as to obtain it substantially free from theprecipitated organic matter, although it is not necessary that theseparated liquor be entirely free from such precipitate. It is advisableto promptly separate the liquor from the precipitated organic matterafter sulfiting to avoid re-solution of the precipitated organic matterwhich takes place to some extent upon prolonged standing in the presenceof the acid. The separated liquor may be used as a cooking liquor, usinga digester which is so constructed as to withstand the action of theacid liquor; or the acid liquor may be neutralized in any suitablemanner, e. g. by adding the required amount of sodium carbonate so thatthe neutralized liquor is alkaline to litmus and only slightly alkalineto phenolphthalin.

The neutralized liquor contains as essential cooking ingredients, sodiumsulfite and sodium thiosulfate. The method of using such a cookingliquor for the production of chemical pulp from wood is more fully setforth in our patent application, Serial Number 7 04,176 filed April 4,1924. For such a cook, the liquor may be tested by titrating it withstandard iodine solution to determine the reactive sulfur compounds,then another portion of the liquor may be treated with an excess ofbarium chloride solution, allowed to settle, and an aliquot portion ofthe clarified liquor removed and titrated with standard iodine solution.The difference in the amount of standard iodine required can be taken asa measure of the amount of sodium sulfite in the cooking liquor. Thecooking liquor may be adjusted in strength so that it contains therequisite amount of sodium sulfite, as set forth in the saidapplication.

This cooking liquor derived from the black liquor may advantageously beemployed for the production of chemical pulp from short fibred woods. e.g. non-coniferous woods The residual liquor or red liquor resulting fromsuch pulping operations may be used, in part, for making up the cookingliquor which contains caustic soda, sodium thiosulfate and sodiumsulfide. The red liquor may also contain some sodium sulfite which maybe so added to the cooking liquor.

The other portion of the red liquor may be concentrated, the driedmatter carbonized in a rotary furnace, e. g. such as is usually used insoda process mills, or it may be charred and then smelted in much thesame way is usually followed in sulfate process mills. The recoveredsoda compounds generally contain a substantial amount of sodiumcarbonate and sodium sulfide, which when treated with lime yield cookingliquors which contain caustic soda and sodium sulfide, and which by theprocess of this invention, may be changed to contain the desired amountof sodium thiosulfate. The organic matter precipitated followingsulfiting contains considerable soda compounds. This material may beadded to the other material undergoing treatment in the rotary furnaceand thus the organic matter destroyed and the soda compounds recoveredalong with those from the untreated residual liquor.

The relatively strong short fibred pulp and the long fibred pulpobtained by the combined cooking operations above described may be mixedand the mixture of pulps used for the production of strong and wellformed papers. Or the pulps may be bleached and used in any mannercustomary in the art. The combined method of operation is particularlyadvantageous where the long fibred woods are resinous coniferous woodswhich grow in the southern portion of the United States of America, andthe short fibred Woods are the gums and other similar trees which growabundantly in the same region.

In the combined operation the soda and the sulfur are used to especialadvantage, the amount of water to be removed by evaporationis'considerably reduced and the use of recovery apparatus is modified inan advantageous manner, with the result that the expense is reduced andthe loss of soda and sulfur is decreased. By using some of thedigesters'in amill for cooking coniferous 1 woods with the stronglyalkaline cooking liquor, and using the black liquor therefrom for theproduction of a cooking liquor which 7 contains sodium sulfite, andusing some of the red liquor for the production of the strongly alkalinecooking liquorand some of the red liquor for mixture with a stronglyalkaline cooking liquor, a number of advantages are obtained.

The paper made fromthe mixture of unbleached long fibred and shortfibred pulp derived in the combined cooking operation has certainadvantages which distinguish it froln paper made exclusively from pulpsfrom coniferous trees.

The following specific description will further illustrate the processof the invention, using the new cookingliquor for the production ofchemical pulp from wood A vertical, stationary type welded steeldigester, about seven feet diameter by 25 feet high overall. is chargedwith about three and a half to four cords of wood, e. g. jack pine inthe form of chips about 7 to inch long along the grain, then about 3,000to 3,500 gallons of cooking liquor is run into the digester. The cookingliquor may contain about 1.500 pounds of caustic soda, about 700 poundsof sodium sulfide and about 700 pounds of sodium t-hiosulfate. The woodchips in the charge may amount to about 10,000 pounds of bone dry Wood.

The digester is provided with a perforated false bottom and withsuitable piping, valves. pump, etc., so that the cooking liquor may bewithdrawn from the lower portion of the digester and circulated incopious amount through the charge in the digester, by rein-- troductionof the cooking liquor in the upper portion of the digester, with meanswithin the upper portion to spread the liquor out above the chips. Steammay be with advantage introduced into the liquor during its passagethrough the circulating pipe line.

The digester may he gradually heated for anhour or so. or until suchtime as the chips are penetrated with cooking liquor to the desiredextent, and thereafter the charge may be further heated until atemperature within the digester of about 170 to 175 centigrade or higheris obtained. Thermometers at va rious points in the digester willindicate whether or not the temperature throughout the charge issubstantially uniform. The heating at the temperature shown above may becontinued until samples of pulp withdrawn through sampling devicesindicate that the cook has been completed. This may require about two tofive hours. depending somewhat upon the cha 'acter of stock desired andupon the other conditions of the cooking operation.

Non-coniferous wood. such as aspen (northern poplar) or dense hardwoods. such as birches. maples. beeches. oaks. et c.. can be cooked in asimilar way. but with these woods the digester charge may with advantagebe heated more rapidlv to the main cooking temperature. it-h all woods,however. it is advantageous to provide thorough circulation of thecooking liquonand to secure uniform treatment and cooking of the entiredigester charge.

The pulps produced by the process of the present invention are ofsomewhat different character from the pulps prodrced bv the usualso-called sulfate process. The replact ment of a part of the caustic orthe sodium sulfide or both with sodium thiosulfate results in a modifiedreaction of the cooking liquor upon the reactive constituents which issomewhat different from the reaction with the ordinary cooking liquor ofthe sulfateprocess, and this is reflected in both the residual liquorand in the pulp produced.

The pulp produced may be used for the manufacture of paper, andespecially when produced from coniferous woods paper of great strengthmay be obtained. Satisfactory pulp can also be produced fromnonconiferous woods, including not cnly the common pulp woods, such aspoplar, but including also the dense heavy hardwoods, such as birches,maples, beeches, oaks, etc. Mixed pulps can also be produced. andespecially unbleached mixed pulps, having advantages in the productionof certain grades of paper.

In the carrying out of a pulpanaking process with a cooking liquorcontaining present invention however provides other.

processes of supplying the sodium content and the sulfur content so thatthe proportion of the different ingredients can be regulated andcontrolled. For example a quantity of sodium sultite or sodiumthiosulfate or a mixture of these can be added to the solution of themelt before causticizing with lime or to the cooking liquor after thecausticization operation and the removal of the calcium carbonate mud.The cooking liquor may also contain other sodium compounds than sodiiuuhydroxide, sodium sulfide, and sodium thiosulfate. By adding aconsiclerable amount of thiosulfate, or by adding elementary sulfur tothe liquor before. during. or after the causticization. an increasedcontent of sulfur in the liquor can be obtained in pro portion to thesodium. Also by treating the solution of the melt or the cooking liquorwith the sulfate. sulfide. sulfite, or the thiosulfate radical or amixture of any of these.

a similar increase in the sulfur content may be obtained. By treatingmilk of lime with elementary sulfur. boiling. separating the solutionfrom the residue. and adding this so lution to the liquor or liquorsreferred to above a precipitate of calcium carbonate may be obtained.and additional sulfur comprunds left in the solution.

e have also shown various ways of controlling the ratio of activesulfur-bearing sodium compounds to other sodium-bearing compoundsespecially caustic soda. We have shown how additional sulfur may beintroduced either in the form of elementary sulfur or of sulfur dioxideor the sulfate or sulfite radical or by using two or more of these formsof sulfur. Ve have shown how the cooking liquor may with advantagecontain sodium thiosulfate in considerable amount in addition to causticsoda and sodium sulfide, either with or without sodiumsuliur compoundssuch as sodium sulfite, etc.

The invention accordingly provides a complete regenerative pulp-makingprocess which is distinguished in important respects from the usualsulfate process so-called. The methods of producing the cooking liquor,the method of carrying out the cooking operation with the particularcooking liquors employed, the method of treating the residual liquorsfor the production of further amounts of cooking liquor therefrom, andother aspects of the invention differentiate it from the usual sulfateprocess; while the process of the present invention presents variousadvartages such as those hereinbefore pointed out.

In the process of the present invention we do not exclude the presenceof varying amounts of sodium sulfite, sodium carbonate, etc.. in thecooking liquor, although sodium sulfite need not be present in anyappreciable amounts.

The process which forms thesubject of the present invention, and whichis more particularly claimed herein, involves the production, and alsothe use of a new cooking liquor containing caustic soda, sodiumthiosulfate, and sodium sulfide, either with or without other chemicalsubstances, and the treatment of the residual liquors from such cookingprocess, for the regeneration of further amounts of cooking liquortherefrom and for the treatment of residual liquors from otherpulp-making operations to produce a regenerated cooking liquor for usein the process of this invention.

We include the use of potassium compounds either alone or in conjunctionwith sodium compounds. In some instances, it is advantageous to usepotassium compounds, especially when the residual liquor is to be usedin the production of fertilizers.

We claim:

1. The method of producing pulp from wood which comprises subjecting thesame to a cooking operation under pressure and at a temperature inexcess of 175 C. with a cooking liquor containing essentially causticsoda, sodium thiosulfate, and sodium sulfide, the amount of caustic sodabeing at least about 40 grams per litre, the amount of sodiumthiosulfate being at least about 10 grams per litre, the amount ofsodium sulfide being at least about 15 grams per litre, and the totalsodium content of the cooking liquor being at least 12% on the bone-dryweight of the wood cooked.

2. The method of producing pulp from wood which comprises subjecting thesame to a cooking operation under pressure and at an elevatedtemperature with a cooking liquor containing essentially caustic soda,sodium thiosulfate, and sodium sulfide, the amount of sulfide being inexcess of the amount of thiosulfate, the amount of reagents being suchthat the residual liquor at the termination of the cooking operation isnon-acid to litmus.

3. The treatment of cellulosic fibre-bearing material which includesdigesting such material with a cooking liquor which contains a compoundalkaline to litmus, separating an alkaline residual liquor from fibrousmaterial and treating the residual uncarbonized liquor with the sulphiteradical, using the resulting solution for the treatment ofcellulose-bearing material, separating the resulting residual liquorfrom the resulting cellulose-bearing material and treating the latterliquor by evaporation of water, carbonization of organic matter, andrecovering a material which contains a sulphide of alkali.

l. The treatment of cellulose-bearing ma terial with a cooking liquorwhich contains caustic alkali, separating the residual liquor andtreating the residual uncarbonized liquor with the sulphite radical,using the resulting solution for the treatment of cellulose-bearingmaterial, separating the resulting residual liquor from the resultingcellulose-bearing material and treating the latter liquor by evaporationof water, carbonization of organic matter, and recovering a materialwhich contains a sulphide of alkali and a carbonate of alkali, treatinga solution of the alkali compounds with calcium hydroxide to produce asolution which contains caustic alkali and alkali sulphide and using theregenerated cooking liquor for the treatment of further amounts ofcellulose-bearing ma terial.

5. The treatment of cellulose-bearing material with a cooking liquorwhich contains alkali sulphide, separating the residual liquor from thefibrous material, treating the residual uncarbonized liquor so as toproduce a cooking liquor containing a trioxy sulfurbearing compound ofan alkali, cooklng cellulose-bearing material with such cooking liquor,separatingt-he resulting residual l1quor from the resultingcellulose-bear ng material and treating the latter liquor so as torecover a material which contains alkali sulphide and using the materialfor the production' of a cooking liquor which contains a sulphide of analkali.

6. The method of obtain ng fibrous material suitable for paper making,which includes the step of digesting wood so as to render individualfibres thereof readily separable from each other by mechanicaltreatment, by means of a liquor the principal reagents of which includesodium combined in the form of sodium hydroxide, a lesser amount ofsodium combined as sodium sulfid and a lesser amount of sodium combinedas sodium thiosulfate, but the total amount of tri-oxy-sulfur-bearingcompounds being less than the total amount of sodium sulfid, the amountof sodium hydroxide being sufiicient to dissolve a substantial part ofthe non-fibrous organic constituents of the wood and in excess of thatrequired to break up the inorganic constituents thereof and thetreatment being adapted to yield a residual liquor at the termination ofthe digest on treatment which is non-acid to litmus.

7. The method of producing chemical pulp from wood which comprisessubjecting the same to a cooking operation under pressure and at anelevated temperature with a cooking liquor containing a caustic alkali,an alkali metal sulfide and an alkali metal thiosulfate, the amount ofsulfide being less than the amount of caustic alkali and theamount ofthio-sulfate being less than the amount of sulfide, but the sulfide andthe thio-sulfate together being greater in amount than the 4 causticalkali.

8. The method of producing pulp from wood which comprises subjecting thewood to a digestion with a liquor including as principal reagents, analkali metal hydroxide, an alkali metal sulfide and an alkali metalthiosulfate, the amount of alkali metal hydroxide being larger than theamount of trioxy-sulfur-bearing compounds.

9. The method of producing pulp from wood which comprises subjecting thewood to a digestion with a liquor includmg as principal reagents analkali metal hydroxide, a sulfide of an alkali metal, and a thiosulfateof an akali metal, the amount of "alkali metal sulfide being reater thanthe amount of alkali metal thlosulfate.

10. The method of producing pulp from wood which comprises subjectingthe wood 7 to a digestion with a liquor including as principal reagentssodium hydroxide, a lesser amount of sodium sulfide and a lesser amountof tri-oxy sulfur-bearing material including sodium thiosulfate.

11. The process of producing pulp, which comprises digesting wood bymeans ofa liquor which contains as its threeessential chemicalingredients sodium hydroxide, sodium sulfid and sodium thiosulfate, the

amount of sodium present in the sodium hydroxide and that present in thesodium sulfid each being larger than that present in the sodiumthiosulfate, and the amounts of hydroxide and sulfid being suificient toren-' der soluble the major portion of the nonfibrous organicconstituents of the wood.

12. The process of producing pulp, which comprises digesting wood bymeans of liquor supplied with an alkali metal hydroxide, an al ali metalsulfid and tri-oxy sulfur-bear-' ing compounds of an alkali metalincluding an alkali metal thiosulfa-te, the amount of alkali metalpresent as hydroxide being larger than that present in tri-oxysulfur-bearin compounds, and the amount of alkali meta sulfid beinglarger than the amount of trioxy sulfur-bearing compounds of an alkalimetal, and the amounts of hydroxide and sulfid being sutficient torender soluble the major portion of the non-fibrous organic constituentsof the wood.

13. The process of producing pulp, which comprises digesting woodbymeans of liquor supplied with an alkali metal hydroxide, an alkali metalsulfid and an alkali metal thiosulfate, the amount of alkali metalpresent as hydroxide being larger than that present as alkali metalsulfid, and the amount of alkali metal present as. sulfid being largerthan that present as alkali metal thiosulfate, and the amounts ofhydroxide and sulfid being suflicient to render soluble the majorportion of the non-fibrous organic constituents of the wood.-

14:. The process of producing pulp, which comprises digesting wood bymeans of liquor supplied with sodium hydroxide, sodium sulfid andtri-oxy sulfur-bearing com ounds of sodium including sodium thiosu fate,the amount of sodium present in the sodium hydroxide being, larger thanthat present in the sodium sulfid, the amount of sodium present in thesodium sulfid being larger than that present in the sodium thiosulfate,the amount of sodium hydrox-vide being at least 40' grams per litre ofthe liquor, the amount of sodium sulfid being at least 15 grams perlitre, the amount of sodium thiosulfatebeing' at least 10 grams perlitre, and the total amount of these reagents being suflicient so thatthe total sodium content thereof is equivalent to at least 12% upon thebone-dry weight of the wood which is treated therewith.

15. The process of producing pulp, which comprises digesting wood bymeans of liquor supplied with sodium hydroxide, sodium sulfidand'tri-oxy sulfur-bearing compounds of sodium including sodiumthiosulfate, the amount of sodium present in the sodium hydroxide beinglarger than that present in the sodium sulfid, the amount of sodiumhydroxide in the liquor being at least 40 but not more than 60 grams perlitre, the amount of sodium sulfid in the liquor being at'least 15 butnot more than 45 grams per litre, the amount of sodium thiosulfate inthe liquor being at least 10 but not more than 30 grams per litre, thesethree reagents being supplied in suliicient amounts so that the totalsodium content thereof is equivalent to at least 12% but not more thanupon the bone-dry weight of the wood treated. v

16. The cyclic process for producing pulp, which comprises digestingcellulosic-fibre- 5' bearing material by means of cooking liquorcontaining as the three essential chemical ingredients sodium hydroxide,sodium sulfid and sodium thiosulfate, the amount of sodium present inthe sodium hydroxide and also that present in the sodium sulfid beinglarger than that present in the sodium thiosulfate; removing residualliquor from the pulp; subjecting the residual liquor to an evaporationtreatment and resulting sodium compounds to a reducing furnacingtreatment to produce sodium carbonate and sodium sulfid, dissolvingthese compounds and treating the solution with material including limeand sulfur-bearing material to produce a regenerated cooking liquorsimilar to the cooking liquor above described; and digestingcellulosic-fibre-bearing material with such regenerated cooking liquor.

17. The process according to claim 16, in which sodium sulfid containedin the solution of sodium carbonate and sodium sulfid 'is treated withthe sulfite radical so as to partially convert it into sodiumthiosulfate, and including such sodium thiosulfate in the saidregenerated cooking liquor that is used in the last-mentioned digestingstep.

18-. The cyclic process of producing pulp, which comprises digestingcellulosic-fibree bearing material by means of cooking liquor;

containing as the three essential chemical in;

and sodium thiosulfate, the amount of sodium present as sodium hydroxideand as sodium sulfid belng larger than that present as so- 450 into theresulting residual liquor, thereby cellulosic-fibre-bearing material bymeans of 5a the regenerated cooking liquor; separating nacing solidsderived therefromso as to decompose organlc matter and obtain a furnaceproduct containing sodium carbonate and sodium sulfid; treating thefurnace product with water and treating sodium carbonate thereof withcalcium hydroxide to form soso dium hydroxide thereby forming anotherre- V fibres; removing water from the residual liqgredients, sodiumhydroxide, sodium sulfid f in the form of sodium carbonate and sodiumdium thlosulfate; removing residual liquorfrom the pulp; introducingsulfur dioxide' which comprises digesting wood bymeans o the resultingresidual liquor from the result ing fibre-bearing material; removingwater Irom the resultlng residual liquor and furobtain a melt containingsodium carbonate and sodium sulfid; treating the melt so as to produce acooking liquor of the type described above, said treatment includingconverting some of the said sodium carbonate into sodium hydroxide bymeans of calcium hydroxide and a treatment of an aqueous liquorcontaining some of the said sodium carbonate and sodium sulfid withsulfur-con taining material adapted to convert a sodium compound of theliquor into sodium thiosulfate; separating the causticized liquor fromundissolved solids; and digesting wood by means of the cooking liquorthus obtained, such cookin liquor containing sodium hygroxide, so iumsulfid and sodium thiosulate.

20. The cyclic process for producing pulp, which comprises digestingwood by means of cooking liquor supplied with sodium hydrox ide, sodiumsulfid and sodium thiosulphate; separating resulting residual liquorfrom the uor; furnacing resulting solids under chemically reducingconditions so as to obtain a furnace product containing its soda. mainlysulfid; treating the furnace product with 1 water to obtain the sodiumcompounds insolution; treating the solution with calcium j hydroxide andwith elementary sulfur to produce a cooking liquor comprising sodiumydroxide and additional sodium sulfid; sep- 1 larating the resultingcooking liquor from un- Udissolved solids; and digesting wood with Q-theresulting cooking liquor.

21. Thecyclic process for producing pulp:

cooking liquor supplied with sodium hydroxide, sodium sulfid and atrioxy sulfur compound of sodium, the amount of sodium present in thesodium hydroxide and the amount {of sodium present in the sodium sulfidbeing larger than that present in the trioxy sulfur compound of sodium;separating the resulting residual liquor from the fibre-bearingmaterial; removing water from the residual liquor by an evaporatingtreatment; subjecting the resulting sodium compounds including anoxy-sulfurcompound derived from theresidual liquor to a smeltingtreatment,thereby obtaining a melt which contains sodium carbonate andsodium sulfid;

dissolving these sodium compounds in water and treating the resultingsolution with elementary sulfur and with calcium hydroxide, therebyobtaining a cooking liquor which contains sodium hydroxide, sodiumthiosulfate and additional sodium sulfid; separating the resultingcooking liquor from result ing lime mud; and digesting wood with theresulting cooking liquor containing the sodium thiosulfate, sodiumhydroxide and sodium sulfid thereby produced.

22, The cyclic process for producing pulp, which comprises digesting'cellulosic-fibrebearing material by means of cooking liquor suppliedwith sodium hydroxide, sodium sulfid and thiosulfateof sodium, theamount of sodium present in the sodium hydroxide being larger than thatpresent in the thiosulfate of sodium; separating the resulting residualliquor from the fibre-bearing material; removing water from theresulting residual liquor by an evaporating treatment; subjecting thesodium compounds including tri-oxy' sulfur-bearing matter derived fromthe residual liquor to a smelting treatment, thereby obtaining a meltthat contains sodium carbonate and sodium sulfid; treating thesecompounds with water to form a solution thereof; supplying the solutionwith elemen tary sulfur and with lime and: treating the solution toobtain a regenerated cooking liquor which contains sodium hydroxide,additional sodium sulfid and sodium thiosulfate; separating theregenerated cooking liquor from the lime mud; and digesting cellulosic-fibre-bearing material with the regenerated cooking liquorcontaining these three compounds of sodium thereby produced.

tures.

LINN BRADLEY. EDWARD P. MOKEEFE 23. The cyclic'process for: producingpulp,

which comprises digesting cellulosic-fibrebearing material by means ofcooking liquor supplied with sodium hydroxide, sodium sulfid and atri-oxy sulfur-bearing compound of sodium, the amount of sodium presentin the sodium hydroxide being larger than that present in the tri-oxysulfur-bearing compound of sodium; separating the resulting residualliquor from the fibre-bearing material removing water from the residualliquor by an evaporating treatment; subjecting resulting solidsincluding carbonaceous matter and a trioxy sulfur compound of sodiumderived from the residual liquor to a smelting treatment, therebyobtaining a melt that contains sodium carbonate and sodium sulfid;treating the melt containing these compounds with water to form asolution thereof; admixing lime with the solution and treating thesolution with material including the-sulfite radical, thereby producinga regenerated cooking liquor which contains sodium hydroxide; sodiumsulfid and a tri-oxy sulfur-bearing compound of sodium; separating theresulting causticized liquor from the resulting lime mud; and digestingcellu-

